<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>默认情况</title>
    <link rel="stylesheet" href="css/style.css">
</head>
<body>
    <div id="father">
        <div id="first">第一个盒子</div>
        <div id="second">第二个盒子</div>
        <div id="third">第三个盒子</div>
    </div>
</body>
</html>